ENH: minor improvements for Enum

- found() method for consistency with other classes

- operator()(name, deflt) for similarity to lookupOrDefault,
  but without a dictionary

src/functionObjects/field/mapFields/mapFields.C

@@ -72,7 +72,7 @@ void Foam::functionObjects::mapFields::createInterpolation
     );
     const fvMesh& mapRegion = mapRegionPtr_();
     const word mapMethodName(dict.lookup("mapMethod"));
-    if (!meshToMesh::interpolationMethodNames_.hasEnum(mapMethodName))
+    if (!meshToMesh::interpolationMethodNames_.found(mapMethodName))
     {
         FatalErrorInFunction
             << type() << " " << name() << ": unknown map method "